Electric coil



13, 1948. A. o. ERICJKSBERG in" AL. 2,434,492

ELECTRIC COIL Original Filed Oct. '7, 1944 INVENTORS. JOSEPH T.OSTE'EPIAN ALVAH O. ERICKSBEJEG I BY 4 AT Of/VEY' Patented Jan. 13, 1948ELECTRIC COIL Alvah 0. Ericksberg, Springfield, and Joseph T. Osterman,Northampton, Mass., assignors to American Bosch Corporation,Springfield, Mass., a corporation of New York Original applicationOctober '7, 1944, Serial No. 557,710. Divided and this applicationAugust 21, 1945, Serial No. 611,788

4 Claims. 1

The present invention relates to electric coils and methods of makingelectric cells on heatresistant coil forms with wire terminals rigidlyfastening the coil winding to the form, by bonding the end turns 01 thewinding to separated conducting areas baked on the form. Such coilsemploy relatively fine wire and are used generally as for instance inspark plugs in ignition systems of the capacitor discharge type,electrical instruments, and radio and other high frequency devices. Thisapplication is a division of our application, Serial No. 557,710, filedOctober '7, i944.

Heretofore it was customary to solder the ends of the coil winding toconducting areas or bands sometimes baked on coil forms to produce thecoil terminals, but this subjected the form to heat shocks of suchnature as often fractured it particularly if silver solder was used, orset up such stresses and strains as resulted in unduly fragile formswhich broke upon ordinary mechanical shock or vibration. Also, theelectric contact between the wire and the conducting areas occurred atspots only, and the surface of the wire at the joints often corrodedin'soldering and sometimes further thereafter so as to be faulty andnonuniform in resistance .upon completion besides deteriorating duringservice. Also the solder sometimes formed lumps and otherwise lackeduniformity in dimensions. which detracted from the smooth and regulardimensions of the terminal in such wise as to prevent reliable contacttherewith in electrical devices and circuits. Furthermore, inapplication to spark plugs in which the coils were impregnated in placeat comparatively high temperature and alsoin service reached acomparatively high temperature at the location of the coil, the solderwould sometimes melt and thereupon interrupt the electrical circuit atone or both terminals of the coil.

In accordance with our'invention, the foregoing difficulties areobviated by bonding the bare end turns of the coil winding to theconducting areas on the coil form by baking adherent metallic materialspread over at least a substantial part of the contacting surfaces ofthe winding while the end turns thereof are held against the conduct-'ing areas. In order to wind closely, insulated wire is used preferably,and to withstand the baking and operating temperatures this insulationis of the heat-resistant type. Preferably the bonding operation, andalso the operation of baking the conducting areas on the coil form, areaccomplished by gradually heating the coil form to the necessarytemperature and thereafter gradually cooling it to room temperature,thereby avoiding 2 the subjection of the coil form to heat shocks and toexcessive stresses and strains. Preferably also the conducting areas onthe coil form constitute end bands of such width as will be covered by anumber of turns of bare wire of the size used. so as to secure rigidterminals of uniform and permanent electrical character. Preferably alsothe same metallic material is used for producing the conducting areas onthe form and for bonding the winding to those areas, since suchsubsequent bonding may then be accomplished at a temperature lower thanis required to produce the conducting areas with the metallic materialthen penetrating the coil form. After the Winding is bonded to theconducting areas to form the coil terminals, it is preferable toadherently coat the terminals with highly conducting material to therebyincrease the electric conductivity thereof.

In such coils, the coil form is preferably cylindrical so as to takeadvantage of the reduced cost of cutting the forms into lengths from along tube. However, in case a spring terminal is required at one end ofthe coil to compensate for changes in dimensions in the deviceincorporating the coil, the form may have an integral cross Wall towhich the spring is riveted. In this latter case the outer face of thecross wall is likewise coated with adherent metallic material at thetime the conducting areas are formed on the outer surface of the form,and the cross Wallis likewise coated with the highly conductivematerial, to thereby produce a good electrical connection between theend of the coil winding and the spring.

Accordingly, one object of the invention is to provide electric coilsand methods of producing electric coils having rigid term nals which aresmooth and of substantially uniform dimensions and of uniform andpermanent electrical characteristics.

Another object is to provide such methods as are applicable to the rapidand uniform production in quantity of inexpensive coils of this kind.These and other objects and advantages of the invention will beunderstood from the following description of two embodiments herein,using as examples ceramic coil forms and insulated wire, taken inconjunction with the accompanying drawings of which each is a centrallongitudinal section partly broken away near its middle portion. In thedrawings:

Fig. 1 shows a cylindrical coil form; Fig. 2 shows the coil form of Fig.1 after conducting bands of adherent metallic material are baked on eachof its ends; Fig. 3 shows the coil form of Fig. 2 after there is woundthereon a coil of of the windin wire having an appropriate number of itsturns at each end bared for bonding to the conducting bands; Fig. 4shows the coil of Fig. 3 after its completion, the end turns of thewinding being connected to the conducting bands by means of adherentmetallic material appropriately baked to mechanically and electricallysecure the winding to the conducting bands to form rigid terminalstherewith, and the terminals being covered with a layer of copperapplied thereto by electrolytic deposition or spraying;- Fig. 5 is anenlarged detail of a completed terminal of Fig. 4; and Fig. 6 shows amodified form of coil of this type provided with a spring terminal.

Referring to the embodiment of Figs. 1-5, the tubular coil form Iconsists preferably of suitable ceramic material as porcelain, such asthat used in sparkplug insulators. Preferably, in order to reduce theircost, the forms are cut from long tubes while plastic before firing, thecorners at 2 of each form being rounded off by tuming or grinding. Afterthe fired coil form, as shown in Fig. 1, bon tetrachloride to removeoil, grease and other foreign material therefrom, each of its ends iscoated by stenciling or in any other suitable way, with a band ofcommercial metallic paint consisting of 90% silver and 10% platinum.Each band is of sufiicient width to underlie about 10-15 turns of wiresubsequently wound on the coil form almost from end to end thereof.These bands are then baked on the coil form by gradually raising itstemperature in a furnace to a value between 1000" F. and 1100" F. duringa period of about 3 to 5 minutes. Then the coil form is gradually cooledto room temperature. Thus in these steps of processing, the coil form isnot subjected to such heat shock, either while the temperature is beingincreased or decreased, as might crack or break it or might produce suchstresses and strains therein as would cause its fracture upon ordinarymechanical shocks or vibration, and the paint is baked into the exteriorpores of the ceramic and completely around the coil form, and if desiredaround its end surfaces also, in sharply defined bands 3 of continuouslyconducting metal of substantially uniform width and thickness.

Instead of using porcelain, other heat-resistant coil forms, as steatiteor glass-bonded mica may be used. Furthermore, the metallic band may bein the form of a paste and may contain pure silver or pure platinum orpure gold or other suitable adherent metallic materials includingadmixtures thereof such that after the baking operation there is noformation of metal oxide having a relatively high electrical resistance.

Having the finished coil form with conducting end bands thereon, asshown in Fig. 2, relatively small copper wire E of a B and S gagebetween No. 30 and No. 42 having a bare diameter of about 10 mils downto about 2.5 mils, is wound thereon substantially from end to end of thecoil form as shown in Fig. 3. Preferably the wire is covered with aninsulation which is a ceramic (inorganic) insulating coating on copper,nickel and other types of wire and which may contain resin and which isa heat-resistant capable of withstanding without change a temperature orat least 600 F. Other insulation materials having suitable heatresisting characteristics may be used if desired. About 10 to turns ateach end 4 depending upon the size of wire making up about the width ofthe bands 3, are bared of its insulation in any suitable way as by isthoroughly cleansed with carscraping. The bare end turns 5 are thengiven a coating of paint, preferably of the same composition as theadherent metallic material of the end bands 3. While these coated turnsare held down tightly against the bands 3 by spring clips or tape, andthe winding 4 on that portion of the coil form therebetween maintainedtight, the wire-wound coil form is bakedin a furnace at a graduallyincreasing temperature up to about 500 F. during a period of 3 to 5minutes, and then gradually cooled, to bond the end turns 5 of thewinding to the bands 3. The spring clips or tapes are then removed. Thistemperature of about 500 F., instead of the baking temperature ofbetween 1000 F. and 1100 F. for the bands 3, suffices for the bondingoperation between the end turns 5 and bands 3 because the first coatingof paint requires a higher temperature for penetration of the ceramicwhile the second coating of paint does not require such penetration butmerely a bond between two contact surfaces. Either before or after thewound coil form has its temperature from the second baking operationgradually reduced to the room temperature, a second and heavier coating6 of the same paint may preferably be baked over the bonded end turns ata gradually rising temperature finally reaching about 500 F. after aperiod of 2 to 2 hours. This additional coating assists in producing aterminal I in which the end turns are rigidly secured to the band in abond of comparatively low electrical resistance capable of withstandinga temperature in service of at least 600 F. Whether or not theadditional coating is applied, the terminals may then, if desired, befurther covered by electrolytically plating them with copper, silver orother highly conducting metal 8 which does not melt at the temperatureto which the coil is subjected in service, or by spraying them withsuitable metal, to thereby further reduce the electrical resistance ofthe terminals. Whether or not the step of electrolytical deposition orspraying is used, each of the terminals 1 so produced is smooth allaround its outer surface and o! uniform dimensions, comprising asubstantially continuous bond between 10-15 shortcircuited end turns ofthe winding. Also, such terminals and windings made in quantity havesubstantially uniform electrical resistance and result in coils ofsubstantially uniform distributed inductants and capacity. Also theterminals are mechanically rigid and not only are non-corroded whencompleted but do not corrode thereafter in such wise as would materiallychange the electrical resistance thereof. Furthermore, due to thegradual application of heat and gradual reduction in temperature. thecoil form is not so apt to be cracked or broken under stresses andstrains such as may result in fracture under ordinary mechanical shockor vibration in handling or service.

In the modification shown in Fig. form 9 has near one end an integralcross wall 10 which is perforated at I I, whereas the remainder of thecoil form is tubular as before. The bond between the bared end turns ofthe winding and the end bands or conducting areas are formed as before,but the initial coating of adherent metallic material is extended overthe inner surface at l2 of the coil form and also over the outer surfaceof the cross wall III, to form a continuous conducting area at that endof the coil form. The spring [3 is electrically fastened to the coilform, preferably after the winding is secured in place, with its endsconnected to the conducting 6, the coil v area on the cross wall by abrass rivet l4. Such a coil, with a spring electrically connected to oneterminal thereof, is useful in mounting in devices, such as spark plugs,having mounting dimensions which are variable within the compensationaffol'ded by the spring l3. Obviously, this electric coil has themechanical and electrical characteristics of the embodiment of Figs.1-5.

It will be apparent that in either of the embodimentsof Figs. l-5 orFig. 6, the wire of the coil may be bare instead of insulated, the turnsthen being maintained in spaced relation in the well known way as byforming in the coil form a helical groove in which the wire is wound.This and other changes and modifications may be made without departingfrom the spirit of the invention as embodied within the broad terms ofthe appended claims.

Having described our invention, we claim:

1. An electric coil comprising a heat-resistant, inorganic coil form,spaced conducting areas on said coil form, said. conducting areascomprising an adherent metallic material, a winding of wire surroundingthe coil form, said winding having bare end portions secured to saidconducting areas and a coating of an adherent metallic material oversaid bare end portions to thereby form bonded terminals for said coil.

2. An electric coil comprising a heat-resistant, inorganic coil form,spaced portions of said coil form having areas coated with aplatinum-silver paint to form conducting areas, a winding of wiresurrounding said coil form and extending over the conducting areas andthe portion therebetween with bare end turns of the winding overlying atleast a portion of said conducting areas and a coating ofplatinum-silver paint over said bare end turns of the winding to therebyrigidly fasten the coil to the coil form.

3. An electric coil comprising a heat-resistant, inorganic coil form,spaced portions of said coil form having areas coated with a highlyconductive material to form conducting areas, a wire winding surroundingsaid coil form and extending over the conducting areas and the portiontherebetween with bare end turns of the winding overlying at least aportion ofsaid conducting areas and a coating of highly conductivematerial over said bare end turns of the winding to thereby rigidlyfasten the coil to the coil form.

4. An electric coil comprising a heat-resistant, inorganic coil form,spaced portions of said coil form having areas coated with a highlyconductive material to form conducting areas, a winding on said coilform over the conducting areas and the portion therebetween with bareend turns of the winding overlying at least a portion of said conductingareas and a coating of highly conductive material over said bare endturns of the winding to thereby rigidly fasten the coil to the coilform, anda resilient terminal secured to said coil form and in contactwith the conducting area thereon.

ALVAH O. ERICKSBERG. JOSEPH T. OSTERMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

